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Tomoya Naito

Publications and source records attributed to Tomoya Naito.

At least 19 recordsLinked to original sources
arXiv2026

Microscopic mechanism of the Fayans pairing for the enhancement of charge radii

The Fayans energy density functional (EDF), and in particular its pairing sector, have been claimed to be able to reproduce the experimental data of charge radii in many instances. A particularly intriguing case is that of the $ \mathrm{Ca} $ isotopes between $ A = 40 $ and $ 48 $, where charge radii exhibit a "bell shape". In our work, we examine the microscopic origin of this behaviour. We prepare in total $ 25 $ paramerizations of the Fayans-like pairing interaction, that are equivalent in fulfilling the same criteria for the reproduction of empirical pairing gaps. We find that both the density and the density-gradient dependence of the pairing interaction are important to reproduce the well-known enhancement of charge radii in the open-shell nuclei, leading to the "bell shape" behaviour of $ \mathrm{Ca} $ isotopes. In particular, this originates from the repulsive nature of the rearrangement potential, and cannot simply be mocked up by a refit of the pairing strength. At the same time, we notice some drawbacks of the Fayans standard EDFs, that may call for investigating a more general form of it.

nucl-th↗
arXiv2026

Comprehensive table of calculated Huff factors

We present a systematic calculation of the Huff factor for nuclei with atomic numbers ($ Z $) in the range of $ 6 \leq Z \leq 94 $. The Huff factor quantifies the increase in the partial lifetime of the decay-in-orbit (DIO) of the muonic atom and serves as an essential correction factor for extracting the nuclear muon capture rate from the measured lifetimes of the muonic atom. However, previous calculations typically provided only the atomic number dependence and neglected isotope dependence -- an assumption whose reliability had not been examined, despite its importance for a comprehensive understanding of the nuclear muon capture rate. In this work, we calculate the Huff factor using nuclear charge distributions obtained from a fully self-consistent microscopic nuclear structure model that incorporates pairing and deformation effects. The resultant Huff factors exhibit a monotonic decrease with increasing $ Z $, while the isotope dependence is found to be small. Our results also show good agreement with previous calculations, supporting the reliability of the present framework. The comprehensive set of Huff factors presented here constitutes the first unified values currently available and will serve as a basis for future evaluations of muon nuclear data.

nucl-th↗
arXiv2026

The Pseudospectral Method for the Dirac Equation with Confining Potential

We observe that solving the Dirac equation for confined potentials using the generalized pseudospectral (GPS) method leads to deteriorating convergence of energy eigenvalues and highly oscillatory in wave functions as the confinement radius decreases. It is found that this issue stems from the first-order differentiation formulation employed in GPS method. Motivated by this insight, we adopt the kinetically balanced generalized pseudospectral method, which incorporates the kinetically-balanced condition into the GPS method. Numerical results demonstrate that the mono-kinetically-balanced generalized pseu dospectral (MKB-GPS) method yields converged energy eigenvalues and generates smooth, continuous wave functions. This is the first application of the MKB-GPS method to confined potentials, and its effectiveness is validated for small confinement radii.

physics.atom-ph↗
arXiv2026

A neural network approach for two-body systems with spin and isospin degrees of freedom

We propose an enhanced machine learning method to calculate the ground state of two-body systems. By extending the original method [Naito, Naito, and Hashimoto, Phys. Rev. Research 5, 033189 (2023)], the present method enables consideration of the spin and isospin degrees of freedom by employing a non-fully connected deep neural network and the unsupervised machine learning technique. The validity of this method is verified by calculating the unique bound state of the deuteron.

nucl-th↗
arXiv2026

Finite-nuclear-size effect for hydrogenlike ions under high external pressure

The influence of pressure on finite-nuclear-size corrections to atomic energy levels and electron-capture decay rate is investigated in confined hydrogenlike ions. The ions are modeled inside an impenetrable spherical cavity, with a Gaussian distribution used to represent the nuclear charge distribution. For each confinement radius used to simulate external pressure, the energies and wave functions of the lowest-lying bound states are determined by numerically solving the Dirac equation via the kinetically balanced generalized pseudospectral method. In contrast to unconfined ions, both the FNS corrections and electron-capture decay rates increase markedly under pressure and exhibit parallel trends with increasing confinement. Pressure also removes level degeneracies and alters the relative magnitudes of FNS corrections across different bound states. Moreover, the nuclear charge radius is found to significantly affect the pressure-enhanced electron-capture decay rate.

physics.atom-ph↗
arXiv2025

Theoretical evaluation of decay mode of $ {}^{229m} \mathrm{Th} $ in solid samples

The excitation energy of $ {}^{229m} \mathrm{Th} $ is extremely low at $ 8.4 \, \mathrm{eV} $; thus, this isotope exhibits changes in its decay modes depending on the chemical state, specifically the outermost electronic states. However, the reported half-lives of the $ γ$-ray transition are not consistent among the previous experiments. In this study, we investigate the chemical states of $ {}^{229m} \mathrm{Th} $ by density functional theory calculations. Based on these results, we evaluate the relationship between the experimental half-life of each sample and the electronic state of $ \mathrm{Th} $. The calculation results indicate that ion trap method, $ \mathrm{Ca} \mathrm{F}_2 $ model and $ \mathrm{Mg} \mathrm{F}_2 $ one decay only via the $ γ$-ray transition, whereas $ \mathrm{Li} \mathrm{Sr} \mathrm{Al} \mathrm{F}_6 $ one decays via the $ γ$-ray transition and has a possibility of decay via internal conversion and electron bridge.

physics.atom-ph↗
arXiv2025

Quartet correlations near the surface of $ N = Z $ nuclei

We theoretically investigate Cooper quartet correlations in $ N = Z $ doubly-magic nuclei ($ {}^{40} \mathrm{Ca} $, $ {}^{100} \mathrm{Sn} $, and $ {}^{164} \mathrm{Pb} $). We first examine the quartet condensation fraction in infinite symmetric nuclear matter by using the quartet Bardeen-Cooper-Schrieffer theory. Together with the total nucleon density profiles of doubly-magic nuclei obtained from the Skyrme Hartree-Fock calculation, we discuss the spatial distribution of quartet correlations in finite nuclei within the local density approximation. Large quartet condensate fractions are found at the surface region of an atomic nucleus due to the strong neutron-proton attractive interaction responsible for the deuteron formation in vacuum. Moreover, we discuss a possible microscopic origin of the Wigner term in the context of nucleon-quartet scattering in dilute symmetric nuclear matter. The nucleon-quartet scattering effect on the Wigner term is numerically estimated to be about one order of magnitude of the total empirical strength, indicating the importance of multinucleon clusters in the symmetry energy and mass formula in addition to the neutron-proton pairing.

nucl-th↗
arXiv2025

Mirror-skin thickness: a possible observable sensitive to the charge symmetry breaking energy density functional

We propose a new observable, named the mirror-skin thickness, in order to extract the strength of the charge symmetry breaking (CSB) term in an energy density functional (EDF). The mirror-skin thickness of $ N = 20 $ isotones and $ Z = 20 $ isotopes is studied by using Hartree-Fock-Bogoliubov (HFB) calculations with various Skyrme EDFs and adding CSB and charge independence breaking (CIB) terms. It is shown that the mirror-skin thickness is sensitive only to the CSB EDF, but hardly depends on either the isospin symmetric part of the nuclear EDF or the CIB term. Therefore, this observable can be used to extract the magnitude of the CSB term in the EDF quantitatively, either from experimental data or ab initio calculations. We have studied the accuracy in the mirror-skin thickness that is needed to extract sensible information. Our study may also help to understand the inconsistency between the strength of the phenomenological CSB and that extracted from ab initio calculations [Naito et al. Nuovo. Cim. C 47, 52 (2024)]. Among possible mirror pairs for experimental study, we propose the mirror-skin thickness between $ {}^{42} \mathrm{Ca} $ and $ {}^{42} \mathrm{Ti} $, which could be accessed in future experiments in RIBF and/or FRIB.

nucl-th↗
arXiv2025

A deep neural network approach to solve the Dirac equation

We extend the method from [Naito, Naito, and Hashimoto, Phys. Rev. Research 5, 033189 (2023)] to solve the Dirac equation not only for the ground state but also for low-lying excited states using a deep neural network and the unsupervised machine learning technique. The variational method fails because of the Dirac sea, which is avoided by introducing the inverse Hamiltonian method. For low-lying excited states, two methods are proposed, which have different performances and advantages. The validity of this method is verified by the calculations with the Coulomb and Woods-Saxon potentials.

quant-ph↗
arXiv2025

Charge symmetry breaking effects of $ω$-$ρ^0$ mixing in relativistic mean-field model

We present a relativistic mean-field model that incorporates charge symmetry breaking (CSB) of nuclear force via $ ω$-$ ρ^0 $ meson mixing, along with corrections to the electromagnetic interaction including the nucleon form factors, first-order vacuum polarization, and Coulomb exchange and pairing terms. The model parameters are refitted using the mass differences of $ T = 1/2 $ mirror nuclei and ground-state properties of magic nuclei, yielding DD-ME-CSB parameter set. The DD-ME-CSB parameter set reproduces the mass differences of mirror nuclei reasonably well up to $ T = 2 $, demonstrating the importance of $ ω$-$ ρ^0 $ mixing. A connection of the present model to a Skyrme-type CSB interaction is also established through a gradient expansion of the energy density functional.

nucl-th↗
arXiv2025

Polaronic neutron in dilute alpha matter: A $p$-wave Bose polaron

We theoretically investigate quasiparticle properties of a neutron immersed in an alpha condensate, which is one of the possible states of dilute symmetric nuclear matter. The resonant $p$-wave neutron-alpha scattering, which plays a crucial role in forming halo nuclei, is considered. This system is similar to a Bose polaron near the $p$-wave Feshbach resonance that can be realized in cold-atomic experiments. Calculating the self-energy within the field-theoretical approach, we give an analytical formula for the effective mass of a polaronic neutron as a function of alpha condensation density. Moreover, two adjacent neutrons in a medium, each of which behaves like a stable polaron having an enhanced effective mass, can form a bound dineutron, with the help of $^1S_0$ neutron-neutron attraction. This is in contrast to the case of the vacuum, where a dineutron is known to be unbound. Our result would be useful for understanding many-body physics in astrophysical environments as well as the formation of multi-nucleon clusters in neutron-halo nuclei.

nucl-th↗
arXiv2025

$ {}^{164} \mathrm{Pb} $: A possible heaviest $ N = Z $ doubly magic nucleus

We confirm by using the Skyrme Hartree-Fock-Bogoliubov calculation that $ {}^{164} \mathrm{Pb} $ is a possible heaviest $ N = Z $ doubly magic nucleus whose lifetime is long enough to be measured on accelerator experiments. We estimate the proton-emission and alpha-decay half-lives of $ {}^{164} \mathrm{Pb} $. The estimated proton-emission half-life ranges from $ 0.1 \, \mathrm{ps} $ to $ 10 \, \mathrm{ns} $, while the alpha decay can be safely neglected.

nucl-th↗
arXiv2024

QCD sum rule approach to Okamoto-Nolen-Schiffer anomaly

A new framework is introduced to connect between a charge symmetry breaking (CSB) energy density functional (EDF) and the low-energy constants derived from quantum chromodynamics (QCD). By constructing a QCD-based CSB EDF, this method provides new insights into the Okamoto-Nolen-Schiffer anomaly, a long-standing puzzle in the energy differences of mirror nuclei that lacks a robust microscopic explanation. Using examples such as $ {}^{17} \mathrm{F} $-$ {}^{17} \mathrm{O} $, $ {}^{15} \mathrm{O} $-$ {}^{15} \mathrm{N} $, $ {}^{41} \mathrm{Sc} $-$ {}^{41} \mathrm{Ca} $, and $ {}^{39} \mathrm{Ca} $-$ {}^{39} \mathrm{K} $, we demonstrate that the proposed interaction effectively resolves the anomaly within the range of theoretical uncertainties.

nucl-th↗
arXiv2024

Accurate and precise quantum computation of valence two-neutron systems

Developing methods to solve nuclear many-body problems with quantum computers is an imperative pursuit within the nuclear physics community. Here, we introduce a quantum algorithm to accurately and precisely compute the ground state of valence two-neutron systems leveraging presently available Noisy Intermediate-Scale Quantum devices. Our focus lies on the nuclei having a doubly-magic core plus two valence neutrons in the $ p $, $ sd $, and $ pf $ shells, i.e. ${}^6$He, ${}^{18}$O, and ${}^{42}$Ca, respectively. Our ansatz, quantum circuit, is constructed in the pair-wise form, taking into account the symmetries of the system in an explicit manner, and enables us to reduce the number of qubits and the number of CNOT gates required. The results on a real quantum hardware by IBM Quantum Platform show that the proposed method gives very accurate results of the ground-state energies, which are typically within $ 0.1 \, \% $ error in the energy for ${}^6$He and ${}^{18}$O and at most $ 1 \, \% $ error for ${}^{42}$Ca. Furthermore, our experiments using real quantum devices also show the pivotal role of the circuit layout design, attuned to the connectivity of the qubits, in mitigating errors.

nucl-th↗
arXiv2024

QCD-based charge symmetry breaking interaction and the Okamoto-Nolen-Schiffer anomaly

An approach is proposed to link the charge symmetry breaking (CSB) nuclear interaction and the low-energy constants in quantum chromodynamics (QCD) by matching the CSB effect in nuclear matter. The resulting CSB interaction is applied to study the Okamoto-Nolen-Schiffer anomaly, still lacking a satisfactory microscopic understanding, on the energy differences of mirror nuclei by taking $ {}^{17} \mathrm{F} $-$ {}^{17} \mathrm{O} $, $ {}^{15} \mathrm{O} $-$ {}^{15} \mathrm{N} $, $ {}^{41} \mathrm{Sc} $-$ {}^{41} \mathrm{Ca} $, and $ {}^{39} \mathrm{Ca} $-$ {}^{39} \mathrm{K} $ as typical examples. The magnitude and sign of the QCD-based CSB interactions are found to resolve the anomaly successfully within theoretical uncertainties.

nucl-th↗
arXiv2023

Multi-body wave function of ground and low-lying excited states using unornamented deep neural networks

We propose a method to calculate wave functions and energies not only of the ground state but also of low-lying excited states using a deep neural network and the unsupervised machine learning technique. For systems composed of identical particles, a simple method to perform symmetrization for bosonic systems and antisymmetrization for fermionic systems is also proposed.

physics.comp-ph↗
arXiv2023

Neural Polytopes

We find that simple neural networks with ReLU activation generate polytopes as an approximation of a unit sphere in various dimensions. The species of polytopes are regulated by the network architecture, such as the number of units and layers. For a variety of activation functions, generalization of polytopes is obtained, which we call neural polytopes. They are a smooth analogue of polytopes, exhibiting geometric duality. This finding initiates research of generative discrete geometry to approximate surfaces by machine learning.

cs.LG↗